Heat shock protein expression in rat skeletal muscle after repeated applications of pulsed and continuous ultrasound

Abstract

Objective: To determine whether repeated ultrasound treatments are capable of increasing the expression of heat shock protein (HSP) 72 and HSP 25 in rat skeletal muscles.

Design: In vivo, experimental, controlled study.

Setting: Animal laboratory.

Animals: Male Sprague-Dawley rats (n=9).

Interventions: Ultrasound (1MHz, 15 min, 2.0 cm2 transducer) continuous at 1.0 W/cm2 spatial average temporal average intensity (CONTUS) or pulsed at 2.0 W/cm2 spatial average temporal peak intensity 50% duty cycle (PULS50) was applied on 4 consecutive days to the lower leg muscles of 1 hindlimb in each rat (n=9).

Main outcome measures: Twenty-four hours after the final ultrasound application, hindlimb muscles were removed, weighed, and assessed for HSP 72 and HSP 25 content by Western blotting. Bands from blots were quantified and data were assessed using t tests (alpha=.05).

Results: Ultrasound did not affect core or contralateral hindlimb muscle temperature. Average muscle temperatures during the final day ultrasound treatments were 38.71 degrees +/-0.30 degrees C when using PULS50 and 38.16 degrees +/-0.57 degrees C when using CONTUS. PULS50 significantly increased HSP 25 content in the plantaris and soleus muscles and HSP 72 content in the plantaris muscles. CONTUS significantly increased HSP 72 content in the white gastrocnemius muscle.

Conclusions: HSPs can be induced in skeletal muscle when ultrasound is used on a repeated basis to treat soft tissue.